This invention relates to a silver halide multilayer photographic element exhibiting improved granularity with linear sensitometric curveshape. In one embodiment the element comprises a dye layered emulsion in the intermediate speed imaging layer of one of the dye image forming units of the element.
Photographic sensitivity can be measured in various ways. One method commonly practiced in the art was first suggested by Hurter and Driffield in the nineteenth century. That method, which is described in numerous references (for example, The Theory of the Photographic Process, 4th edition, T. H. James editor, Macmillan Publishing Co., New York, 1977), is to expose an emulsion coated onto a planar substrate for a specified length of time through a filtering element, or a step tablet interposed between the coated emulsion and light source. The step tablet modulates the light intensity in a series of uniform steps of constant factors by means of the constructed increasing opacity of the filter elements of the tablet. As a result the exposure of the emulsion coating is spatially reduced by this factor in discontinuous steps in one direction, remaining constant in the orthagonal direction. After exposure for a time required to cause the formation of a developable image through a portion, but not all of the exposure steps, the emulsion coating is processed in an appropriate developer, either black and white or color, and the densities of the image steps are measured with a densitometer. A graph of the exposure on a relative or absolute scale, usually in logarithmic form, defined as the irradiance multiplied by the exposure time, plotted against the measured image density created during development, can then be constructed. The graph so produced, often referred to as the characteristic profile or HandD (see FIG. 1 in U.S. Pat. No. 5,314,793), demonstrates the way in which an emulsion responds to exposure and development and provides valuable insight into the photographic performance to be expected from the imaging element.
The characteristic profile in negative working photographic silver halide systems typically has an xe2x80x9csxe2x80x9d shape. The displacement of the characteristic profile above zero density is referred to as minimum density (Dmin) or fog. Depending on the purpose, a suitable image density on the characteristic profile is chosen as a reference (for example 0.15 or 0.20 density above that formed in a step which received too low an exposure to form detectable exposure-related image). The exposure required to achieve that reference density can then be determined from the constructed graph, or its electronic counterpart. The inverse of the exposure to reach the reference density is designated as the emulsion coating sensitivity S. The value of log10S is termed the speed. The exposure can be either monochromic over a small wavelength range or consist of many wavelengths over a broad spectrum as already described. Typically as exposure onto an emulsion coating is increased, at some point the characteristic profile curve rolls over and produces no further increase in density with increased exposure. The maximum density of the characteristic profile is referred to as Dmax. The displacement along the exposure scale of the characteristic profile between the first incremental density above Dmin and the last incremental density before Dmax defines the exposure latitude. The longer the exposure latitude the lower the risk of image information being lost through over or under exposure during imaging. An average photographic scene is spread out over an exposure latitude of about 1.2 logE (4 stops). Critical scenes containing both dark shadows and reflective highlights can contain information spread out over a much larger exposure latitude. An exposure latitude of 1.8 logE (6 stops) offers sufficient margin for recording extremely demanding scenes. The slope or gamma of the characteristic profile (delta density/delta Log Exposure or first derivative of the HandD curve) is usually measured over some segment of the curve bridging mid-scale density. Silver halide photographic films also strive to maximize the linearity of the mid-scale density portion of the characteristic profile. A long linear mid section of the characteristic profile means that the film will have a predictable and desirable linear relationship between exposure and density over many varied levels of exposure.
Although the image dye characteristic profile of color multilayer photographic element is useful in assessing imaging capability and quality, one important image property that requires separate inquiry is image noisexe2x80x94i.e., granularity. It is a long-standing objective of color photographic origination materials to maximize the overall response to light while maintaining the lowest possible granularity. Increased photographic sensitivity to light (speed) allows for improved image captured under low light conditions or improved details in the shadowed regions of the image. Sensitivity is much more important with origination materials than with print materials, the latter depending entirely on operator supplied light. In general, the overall light sensitivity provided by the light sensitive silver halide emulsions is a function of the size of the emulsion grains. Larger emulsion grains capture more light. Upon development, the captured light is ultimately converted into dye deposits that constitute the reproduced image. The granularity exhibited by these dye deposits is directly proportional to the grain size of the silver halide emulsion. Larger silver halide emulsion grains have higher sensitivity to light but also lead to higher granularity in the reproduced image.
As the photographic industry evolves, conventional film and digital technology coexist as tools to both capture and manipulate information. Information captured on film is now often scanned and digitally manipulated before it is outputted to a final display format. Maximizing exposure latitude, enhancing the curveshape linearity and granularity (signal to noise) of photographic origination film lessens the amount of work needed to correct and manipulate digitally scanned film information. Co-optimizing to these performance characteristics expands the capabilities of photographic film as an image capture and recording media.
J-aggregating cyanine dyes are used in many photographic systems. It is believed that these dyes adsorb to a silver halide emulsion and pack together on their xe2x80x9cedgexe2x80x9d which allows the maximum number of dye molecules to be placed on the surface. However, a monolayer of dye, even one with a high extinction coefficient as a J-aggregated cyanine dye, adsorbs only a small fraction of the light impinging on it per unit area. The advent of tabular emulsions allowed more dye to be put on the grains due to increased surface. However, in most photographic systems, it is still the case that not all the available light is being collected. Increasing the light absorption cross-section of the emulsion grains can lead to an increased photographic sensitivity. The need is especially great in the green sensitization of the magenta layer of color negative photographic elements. The eye is most sensitive to magenta dye and this layer has the largest impact on image structure (e.g., granularity) and color reproduction. High speed in this layer can be used to obtain improved color and image quality characteristics.
One way to achieve greater light absorption is to increase the amount of spectral sensitizing dye associated with the individual grains beyond monolayer coverage of dye. Some proposed approaches are described in the literature by G. R. Bird, Photogr. Sci. Eng., 18, 562 (1974). One useful method is to have two or more dyes form layers on the silver halide grain. Penner and Gilman described the occurrence of greater than monolayer levels of cyanine dye on emulsion grains, Photogr. Sci. Eng., 20, 97 (1976): see also Penner, Photogr. Sci. Eng., 21, 32 (1977). In these cases, the outer dye layer adsorbed light at a longer wavelength than the inner dye layer (the layer adsorbed to the silver halide grain). Bird et al. in U.S. Pat. No. 3,622,316, described a similar system. A requirement was that the outer dye layer absorb light at a shorter wavelength than the inner layer. The problem with early dye layering approaches was that the dye layers produced a very broad sensitization envelope. This would lead to poor color reproduction since, for example, the silver halide grains in the same color record would be sensitive to both green and red light.
More recently Parton et al. (U.S. Pat. Nos. 6,143,486 and 6,165,703) disclosed a more practical approach to form more than one layer on silver halide emulsion grains that can afford increased light absorption. These dye layers are held together by a non-covalent attractive force such as electrostatic bonding, van der Waals interactions, hydrogen bonding, hydrophobic interactions, dipole-dipole interactions, dipole-induced dipole interactions, London dispersion forces, cationxe2x88x92xcfx80 interactions, etc., or by in situ bond formation. The inner dye(s) is absorbed to the silver halide grains and contains a least one spectral sensitizing dye. The outer dye layer(s) (also referred to here in as an antenna dye layer(s)) absorbs light at an equal or higher energy (equal or shorter wavelength) than the adjacent inner dye layer(s). The light energy emission wavelength of the outer dye layer overlaps with the light energy absorption wavelength of the adjacent inner dye layer. A particularly useful configuration involves silver halide grains sensitized with at least one dye containing at least one anionic substituent and at least one dye containing at least one cationic substituent, wherein the dye layers are held together by non-covalent forces or by in situ bond formation. The application of layered dye technology has focused primarily on improving photographic sensitivity (speed) of the fastest emulsion components with minimal granularity penalty.
It is a fundamental problem in modern color photography to minimize signal to noise (granularity) of a silver halide element while maximizing light sensitivity (speed), exposure latitude and linearity of the photographic response curve (characteristic profile).
This invention provides a silver halide photographic element comprising a support bearing a cyan dye image-forming unit comprised of at least one red-sensitive silver halide emulsion layer having associated therewith at least one cyan dye-forming coupler, a magenta dye image-forming unit comprising at least one green-sensitive silver halide emulsion layer having associated therewith at least one magenta dye-forming coupler, and a yellow dye image-forming unit comprising at least one blue-sensitive silver halide emulsion layer having associated therewith at least one yellow dye-forming coupler, wherein said photographic element has an ISO speed rating of 800 or greater and has an integrated RMS green granularity equal to or less than 11.2.
It further provides a silver halide photographic element comprising a support bearing a cyan dye image-forming unit comprised of at least one red-sensitive silver halide emulsion layer having associated therewith at least one cyan dye-forming coupler, a magenta dye image-forming unit comprising at least one green-sensitive silver halide emulsion layer having associated therewith at least one magenta dye-forming coupler, and a yellow dye image-forming unit comprising at least one blue-sensitive silver halide emulsion layer having associated therewith at least one yellow dye-forming coupler, wherein at least one of the dye image forming units contains layers of differing sensitivities, said layers comprise at least a slow, a fast and an intermediate layer and the layer of intermediate sensitivity contains a silver halide emulsion comprising silver halide grains having associated therewith at least two dye layers comprising (a) an inner dye layer adjacent to the silver halide grain and comprising at least one dye, Dye 1, that is capable of spectrally sensitizing silver halide and (b) an outer dye layer adjacent to the inner dye layer and comprising at least one dye, Dye 2, wherein the dye layers are held together by more than one non-covalent force; the outer dye layer absorbs light at equal or higher energy than the inner dye layer; and the energy emission wavelength of the outer dye layer overlaps with the energy absorption wavelength of the inner dye layer. In one embodiment the magenta dye forming layer comprises the dye layered emulsion.
The photographic elements of this invention demonstrate improved granularity at high speeds. They further demonstrate improved linearity. This advantageous co-optimization of photographic sensitivity, granularity and linear exposure latitude was a completely unexpected advantage of utilizing dye layering in the intermediate record of a color negative film. These improved performance characteristics are particularly valued in consumer and professional color negative as well as color negative motion picture origination films where high magnification and digital scanning applications continue to push the demands for improved images structure.